Centrifugal switch.



c. L. KENNEDY. CENTRIFUGAL SWITCH. APPLICATION FILED AUG.1| 1914.

1,222,633. Patented Apr. 17,1917.

uni-mum mm I 19 mmm WITNESSES: INVENjTOR WW 6 w BY ATTORNEY.

UNITED STATES PATENT OFFICE.

CARLTON L. KENNEDY, OF SOUTH BBAINTREE, MASSACHUSETTS, ASSIGNOR TO THE HOLTZER-CABOT ELECTRIC COMPANY, OF BROOKLINE, MASSACHUSETTS, A COR- PORATION OF MASSACHUSETTS.

CENTRIFUGAL SWITCH.

Specification of Letters Patent.

Patented Apr. 17, 1917.

Application filed August 1, 1914. Serial No. 854,523.

To all whom it may concern:

Be it known that I, CARLTON L. KEN- NEDY, a citizen of the United States, residing at South Braintree, in the county of Norfolk and State of Massachusetts, have invented certain new and useful Improvements in Centrifugal Switches; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The present invention relates to improvements in centrifugal switches and more particularly to centrifugal switches for splitphase induction motors. This type of motor employs two sets of windings upon the primary or stator. One winding, called the working winding is permanently connected with the current supply while the motor is operating. The other winding, called the starting winding is connected in series with a centrifugal switch and is used only to start the motor, being open-circuited When the motor has attained a predetermined speed.

A type of switch commonly used consists of brush arms which are mounted upon one end of the armature and which contact with and revolve around contact rings which close the circuit through the starting winding and are mounted side by side and secured to the motor frame. While the armature is getting under way from a condition of rest the contact rings are electrically connected by means of the brush arms, but when the armature has attained the required velocity, the brush arms are acted upon by centrifugal force and the electrical connection broken. Centrifugal switches of this construction have hitherto proven defective by reason of the fact that in order that the brush arms might respond readily to centrifugal force, it has been necessary to make them somewhat heavy, and, consequently, in order that the brush arms might not fly out of contact with the contact rings before the motor has attained the required speed, the springs holding them in contact with the rings must necessarily be of sufiicient strength and tension to prevent the premature disconnection. These heavy brush arms acted upon and held normally upon the contact rings by heavy springs tend to score channels in the metal of which the rings are composed, causing them and the brush arms to wear away rapidly.

On the other hand, if brush arms of too light a construction are used and are held normally in contact with the contact rings by springs of light tension so as to avoid any possibility of scoring, the electrical connection is liable to prove faulty by reason of dirt collecting on the contact surfaces. The brush arms also are easily bent and forced out of alinement with the rings. Moreover, brush arms of light construction do not respond readily to centrifugal influence, with the result that disconnection between the contact rings and the centrifugal switch at the proper time is not positively assured.

One object of this invention is to eliminate scoring of the contact rings by the brush arms. Another object is to secure a good electrical contact between them while the motor is coming up to speed; and a third object of the invention is to insure the positive disconnection between the contact rings and the brush arms at the proper time. These objects are accomplished by pivoting two brush arms of light construction upon a weight arm which is adapted to be acted upon by centrifugal force and at the critical speed to knock the brush arms out of contact with the contact rings. The tension of the spring which holds the brush arms in contact with the rings is adjusted and proportionately distributed between the weight arm and the brush arms so that the former may not prematurely open circuit the starting winding, and so that the latter may not score channels in the rings. The life of the rings and the brush arms is, therefore, greatly lengthened. Other ob jects of the invention will hereinafter appear.

In the accompanying drawings illustratis secured, through the holes at, to and properly insulated from one end of the armature and consists of a weight arm 5 pivoted to the switch support at 6, and two brush arms 7 and 8 pivoted at 9 on an inward projection of the weight arm and being disposed on both sides thereof. A counter Weight 10 made integral with the switch support coun terbalances the weight and brush arms. The contact rings 11 and 12 are mounted side by side upon a spider 13 in the shape of a cross formed of four legs 14: which project radially at right angles to each other, two each from the basal extremities of each of the rings. The manner of insulating the two rings from each other. is shown in Fig. 5. The legs 14 are secured through the holes 17, with proper insulation to the motor frame. The contact rings project through the hole 18 of the switch support so that the surface of the ring 11 is in alinement with the arm 8 and the surface of the ring 12 is in alinement with the arm 7.

The centripetal movement of the weight arm is limited by the stud stop 15 and its centrifugal movement by the stop 16. The weight arm is normally held against the stop 15 by means of the spring 19, one end of which is fastened to the stud 20 projecting from the support, and the other end connected with a pin 21 which passes through and is secured to the two brush arms. The spring 19 holds the inner or contact ends 23 of the brush arms lightly in contact with the contact rings, and the free or outer .end 2% of the weight arm against the stop 15. Now it is obvious that the pressure of the brush arms upon the contact rings is-much less than the pressur of the weight arm upon the stud 15. The difference in the two pressures is proportional to the difference-in length of the perpendiculars dropped from the pivots or ful crums 6 and 9 upon a straight line drawn through the hole in the stud 20 and the pin 21, allowing, of course, for the difference in distance respectively between the contacting points of the arms and their pivots. By changing the position of the pin 21 the pressures of the arms at their points of contact may be varied according to the requirement of any given condition. In centrifugal switches of the old type of construction, the pressure of the weight arm (which is now expended against the stop 15) used to be directly expended upon the contact rings. In the centrifugal switch of this invention the pressure exerted by arms which contact with the contact rings is reduced until it is just suiiicient to insure a good electrical contact, thereby reducing the wear on the contact rings to a minimum. The cost of replacing worn out contact rings and brush arms is, therefore, made negligible.

Fig. 2 shows the position of the operative members of the switch while the motor is stationary. Immediately upon the starting up of the motor, the outer end of the weight arm, under the influence of centrifugal force, tends to fly toward the stop 16, carrying with it the brush arms. The contact ends of the brush arms, however, still remain in contact with the contact rings and continue to contact with the rings until the pin 26, secured to and brojecting from both sides of an inward protuberance of the weight arm, has reached them. This is because the brush arms turn on their pintles 9; and because the pressure of the spring 19 is stronger than the centrifugal force generated in the weight arm by the speed thus far attained. The counter-balancing ends 27 of the brush arms also aid in maintaining the contacts. But when the speed of the motor has reached a predetern'iincd point, the weight arm has traveled outwardly a suflicient distance to bring the pin up nearly to the inner surface of the brush arms; and then as the weight arm continues its outward travel with constantly accelerating velocity the brush arms are struck a percussive blow by the pin 26 and lifted suddenly out of contact with the contact rings and the starting winding is thereby open-circuited. If for any reason the brush arms should fail to turn 011 their pintles 9 as by reason of sticking, for example, unre sponsive to the action of the spring 19, and consequently during the entire outward travel move with the weight arm instead of only at the latter end of the outward travel of the weight arm, they will bring up against the guards 29 which project inwardly from the stud 16. It will be observed, however, that by the time the pin 26 has reached the brush arms, the depression 30 of the weight arm will have brought up against the stud 16. M

What I claim is:

1. A centrifugal switch having, in combination, a contact ring, a rotary support, a weight arm mounted on the support movable outwardly under centrifugal force, a brush arm mounted on the weight arm, and a spring connected with the support and with the brush arm for normally holding the weight and brush arms inwardly with the latter against the contact ring.

2. ii. centrifugal switch having, in combination, a contact ring, a rotary support, a weight arm pivoted on the support, a brush arm pivoted on the weight arm, the brush arm being adapted to contact with the contact ring while the weight arm is moved outward under centrifugal force until the rotary support has reached a predetermined speed of rotation, and a spring connected with the support and with the brush arm.

3. A centrifugal switch having, in combination, a contact ring, a "rotary support, a weight arm pivoted on the support, a brush arm pivoted on the weight arm, and means directly connecting the brush arm with the rotary support for holding the brush arm in contact with the contact ring while the weight arm is moving outwardly to a prede termined point.

4.. A centrifugal switch having, in combination, a contact ring, a rotary support, a weight arm pivoted on the support, and a brush arm pivoted on the weight arm and adapted to be held in contact with the contact ring by means of a spring, the brush arm being further adapted to be lifted out of contact with the ring by the weight arm when the support has attained a predetermined speed of rotation.

5. A centrifugal switch having, in combination, a contact ring, a rotary support, a weight arm pivoted on the support, a brush arm pivoted on the weight arm and normally in contact with the contact ring and adapted to remain in contact with the contact ring while the weight arm is traveling outward under centrifugal force, until the support has attained a predetermined speed of rotation, and then to be knocked out of contact with the ring by the weight arm.

6. A centrifugal switch having, in combination, a contact ring, a rotary switch support, a weight arm mounted on the support, a brush arm mounted on the weight arm and normally in contact with the ring, and means carried by the weight arm for knocking the brush arm out of contact with the contact ring when the support has reached a predetermined speed of rotation.

7. A centrifugal switch having, in combination, a contact ring, a rotary switch sup port, a centrifugal member mounted on the support and arranged to move outward under the action of centrifugal force, a brush mounted on the centrifugal member, and means tending to hold the brush and centrifugal member in inward position, said centrifugal member and brush having provision by virtue of which the centrifugal member lifts the brush from the contact ring beginning after the centrifugal member has attained substantial velocity of outward movement.

8. A centrifugal switch having, in combination, a contact ring, a brush held against the contact ring with a light yielding force, a weight held inward by a stronger yielding force and arranged to be thrown outward by centrifugal force to lift the brush from the ring, and means acting directly on the brush arm and indirectly on the weight arm for exerting the light yielding force on the former and the stronger yielding force on the latter.

9. A centrifugal switch having, in combination, a contact ring, a rotary support,

a centrifugally operated weight movably mounted on the support, a brush mounted on the weight, and means directly connecting the brush with the rotary support for holding the brush in contact with the contact ring during the initial centrifugal movement of the weight.

10. A centrifugal switch having, in combination, a contact ring, a brush, yielding means for holding the brush in contact with the ring, and a centrifugally operated weight upon which the brush is mounted having a limited movement independent of the brush and arranged to move the brush, by a percussive engagement therewith, out of contact with the ring.

11. A centrifugal switch having, in combination, a contact ring, a rotary support, a stop thereon, a weight arm pivotally mounted on the support and normally resting against the stop, a brush arm pivoted on the weight arm having its free end normally in engagement with the contact ring and having its pivot located between the weight arm pivot and the point of contact between the contact ring and the brush arm, and a spring connected to the support and to the brush arm between the brush arm pivot and the point of contact between the brush arm and the contact ring.

12; A centrifugal switch having, in combination, a stationary contact ring, a rotary support, a centrifugal member movably mounted on the support, a movably mounted brush arm on the centrifugal member, and a spring acting directly on the brush arm and indirectly on the centrifugal member for normally holding the centrifugal member in inward position and for holding the brush arm in contact with the contact ring, said brush arm and centrifugal member being constructed and arranged so that greater force is required to move the latter outwardly than the pressure of the brush arm against the contact ring.

13. A centrifugal switch having, in combination, a stationary contact ring, a rotary support, a. stop thereon, a weight arm mounted on the support, a brush arm mounted on the weight arm, and single means for holding the weight arm against the stop and the brush arm against the contact ring until the rotary support reaches a predetermined speed.

14. A centrifugal switch having, in combination, a stationary contact ring, a rotary support, a centrifugal member movably mounted on the support, a movable contact member mounted on the centrifugal member, and means for holding the centrifugal member and the contact member in inward position, said centrifugal member having a pin for engaging and lifting the contact member off of the contact ring.

15. A centrifugal switch having, in comthrough the brush arm indirectly on the bination, a stationary contact ring, a rotary Weight arm for holding the weight arm insupport, a Weight arm pivoted on the sup- Wardly With greater force than the brush 10 port and adapted to be moved outwardly by arm is held against the contact ring.

centrifugal force, a brush arm mounted on CARLTON L KENNEDY the Weight arm and normally held in engagement With the contact ring, and a spring Vitnesses:

acting directly on the brush arm and GEO. E. STEBBINS,

Arron AOKROYD,

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

